Summary:
Deposits of this type are referred to in many ways, such as; gold quartz veins or lodes, mesothermal gold, shear-hosted or shear zone gold, orogenic gold, syn-orogenic veins, Mother Lode gold, etc.
Locally, these deposits occur primarily as quartz veins, stockworks or stringer zones in fault, fracture and shear zones and are typified by the variability of host rocks which are affected by pervasive carbonatization with localized sericitization and sulfidation marginal to gold-bearing quartz veins.
In the Yellowjacket Zone, ophiolite-hosted gold quartz veins stockworks or breccias are contained within faultbounded lenses of oceanic igneous crust. Listwanite altered ultramafic rocks are consistently associated with the ophiolite-hosted gold veins, but rarely host them. This deposit type contains very high grade, coarse native gold occurring in quartz veins or flooding hosted by ophiolitic mafic igneous crustal rocks (gabbro, diabase, basalt, andesite) adjacent to listwanite altered ultramafic rocks.
Placer deposits in the camp are situated in stream valleys cutting erosional windows through the carbonatized relatively flat lying thrust faults within the Atlin ophiolitic assemblage.
Historically, significant economic concentrations of placer gold are restricted to streams in the Pine Creek and McKee Creek watersheds. It appears that preferential erosion through flat-lying mineralized thrust contacts in both these areas was accelerated along high-angle, post accretionary fault zones. This interpretation is supported by the presence of fault breccia zones within both these valleys.
Lode gold mineralization associated with the thrust sheet of ultramafic cumulate rocks includes showings hosted by faults bounding this thrust sheet, including the Yellowjacket, Imperial, Surprise and Lakeview (see Adjacent Properties section). The Yellowjacket showing is associated with the basal faulted contact of this ultramafic body along the Pine Creek valley. The contact between the hangingwall ultramafites and footwall metabasalts is not exposed but is well defined by exploration drill holes (Marud, 1988). The zone of thrusting is characterized by up to 15 metres of carbonate alteration that contains intermittent zones of quartz-carbonate veining in both hangingwall and footwall rocks.
On the Atlin Gold Property the thrust fault is disrupted by a later, east-trending, steeply dipping structure referred to as the Pine Creek Fault. This high angle fault zone averages approximately 70 metres in width and can be described as a fault breccia. The fault is characterized by strongly broken and fractured rocks, with gouge and rubble zones ranging from centimetres to more than 10 metres wide. The zone contains irregular blocks and lenses of all the lithologies that are typical of the Atlin ophiolitic assemblage, metamorphosed basalt, diabase, gabbro and ultramafics as well as younger felsic rocks. Ultramafic rocks vary from completely serpentinized to completely carbonatized, with or without quartz veining.